1. Field of the Invention
The present invention is directed to an accumulating conveyor upon which articles may be stored or accumulated to be advanced to a work station only when the work station is ready to receive an article.
2. Description of the Prior Art
A typical application of such conveyor is in a production line where, due to the nature of an operation performed on the article at the work station, the rate at which articles are discharged from the work station is a variable rate or a rate which is less than the rate at which articles can be supplied to the work station. When the work station is occupied, the conveyor functions to halt the flow of articles to the work station, thus accumulating a line of articles upstream from the work station so that articles can be supplied to the work station as fast as the work station is ready to accept them. The basic requirement of such a conveyor is that it must be able, while being continuously operated to advance articles intermittently in accordance with the requirements of the work station.
In the prior art, a walking beam type conveyor is conventionally used to perform the foregoing function. Uniformly spaced article receiving seats are located along the fixed frame of the conveyor and a lift-and-carry mechanism is associated with each seat which is operable in a cyclic sequence to lift and carry an article from one seat to the next advanced seat to advance the articles in step-by-step movement along the conveyor. The various lift-and-carry mechanisms are interlinked with each other so that only those lift-and-carry mechanisms which are upstream from an empty seat will be actuated to advance articles in an operating cycle. Prior art examples of such conveyors are found in U.S. Pat. Nos. 4,441,606 and 4,240,542.
While the walking beam type accumulating conveyor is widely used, it possesses certain inherent drawbacks. A lift-and-carry mechanism must be provided at each station, together with a sensing mechanism at each station which detects the presence or absence of a part or article at that station and signals all upstream stations as to whether they are to act in the transfer or non-transfer mode during the next cycle. The intermittent step-by-step operation relies upon a reciprocatory drive mechanism which subjects a multitude of interconnected system parts to impact loading at stroke reversal and which is subjected to variable loading, depending upon the number of parts which are to be advanced, upon the actuating stroke. The articles conveyed in turn must be bodily lifted from the conveyor frame, advanced, and then lowered gently back onto the conveyor frame a substantial number of times in order to transmit the conveyor.
The accumulating conveyor of my U.S. Pat. No. 4,598,818 was designed to overcome these problems. It employs a pair of multiple strand roller chains operatively trained about paired end sprockets for coordinated movement along an endless path having horizontal upper and lower runs extending between the end sprockets. One strand of each roller chain is operatively trained about one set of end sprockets while a second strand of each chain is supported laterally clear of the end sprockets and track means employed to support and guide the chains along their upper by lower runs. A plurality of article carriers are mounted to extend between the two chains and to be supported from the second strands of the chains by outer and inner support plates fixedly mounted at the opposite sides of each carrier. The outer support plates support the carriers upon the chains during transit of the upper run while the inner support plates suspend the carriers in an inverted position during transit of the lower run by the frictional engagement of chain engaging edges on the plates with the chain rollers. The chain is continuously driven and, because of the frictional coupling between the carriers and chains, carriers may be accumulated or held stationary by suitable stops at selected locations along either the upper and lower run.
To transfer carriers around the curved portions of the chain path defined by the end sprockets, the spacing and configuration of the opposed edges of the inner and outer support plates are designed to automatically positively couple the carrier to the chain as the carrier moves from the upper or lower run into the curved portions of the chain path.
The length of the straight edge section of the inner plate, its spacing from the opposed straight edge section of the outer plate, and the inclination of the beveled edge sections of the inner plate are related to the end sprocket radius and the pitch of the chain in a fashion such that when the carrier moves onto the curved portions of the endless path defined by the end sprockets, the corners at the junctures of the straight edge section and beveled edge sections of the inner plate project into the spaced between two adjacent rollers of the chain and are positively held in this position by the tangential engagement of the straight edge of the outer plate with a roller midway between those two sets of rollers engaged by the inner plate. This action provides a positive coupling between the carrier and the chain as the carrier transmits the curved portions of the endless path so that the carriers can be transported from the lower run upwardly around one set of end sprockets to the upper run and be restricted to movement with the chain as the carrier is passed downwardly around the other end sprockets from the upper run to the lower run.
My U.S. Pat. No. 4,681,212 represents a further refinement to the above described system. In the U.S. Pat. No. 4,681,212, the carrier is positively coupled to the chains during transit of the curved portions of the path defined by the sprocket means by concave recesses at opposite ends of the straight edge section of the inner support plate. The rollers of the chain are seated and held by the tangential engagement of the straight edge of the opposed outer plate with a roller intermediate the seated rollers.
While the accumulating conveyors disclosed in my above-referenced patents are successful in overcoming the problems cited with the prior art, they do require that the spacing between the chain engaging edges, the length of the straight edge section and beveled edge sections of the inner plate, the radius of the sprocket means, the pitch of the chains, and the size of the concave recesses exhibit particular and fixed relationships to each other. Hence, the tolerance permitted in the sizes and spacings of the various components is relatively small. This factor can make these conveyors relatively expensive to manufacture and difficult to set up and operate.
The present invention is designed to overcome this problem.